The anti-theft device known heretofore lock the steering wheel of a vehicle as long as the user does not turn the switch key in the direction necessary to start the engine. It is known that with such devices it is easy to start the engine without using the switch key. As a matter of fact, it is only necessary to cut off the wires connected to the terminals of the known anti-theft device, and then to short-circuit them.
An object of the present invention is to obviate such drawbacks of the known devices by providing a simple and inexpensive device which prevents the electric start of the engine by releasing or activating an alarm in the event of an attempt to steal the car.